U.S. patent application number 16/173369 was filed with the patent office on 2020-04-30 for small arms cartridge.
The applicant listed for this patent is Abram W. Boyd Summerfield. Invention is credited to Pietro Boyd, Raymond L. Dennis, Abram W. Summerfield, Kristofer Wisdom.
Application Number | 20200132421 16/173369 |
Document ID | / |
Family ID | 70326188 |
Filed Date | 2020-04-30 |
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United States Patent
Application |
20200132421 |
Kind Code |
A1 |
Summerfield; Abram W. ; et
al. |
April 30, 2020 |
SMALL ARMS CARTRIDGE
Abstract
Provided is a centerfire rifle cartridge. A case has a head end,
an open mouth end for receiving a projectile, and a central axis.
The head end has a base portion substantially conforming to that of
a .50 BMG cartridge. The case has a case wall with a taper of up to
1.0.degree. relative to the central axis. A frusto-conical shoulder
portion extends from the case wall and has an angle of
approximately 40.degree. relative to the central axis. A neck
portion extends from the shoulder portion and has a mouth sized to
receive a .375 caliber (9.5 mm) projectile.
Inventors: |
Summerfield; Abram W.;
(Orofino, ID) ; Boyd; Pietro; (Moscow, ID)
; Wisdom; Kristofer; (Orofino, ID) ; Dennis;
Raymond L.; (Hindmarsh, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Summerfield; Abram W.
Boyd; Pietro
Wisdom; Kristofer
Dennis; Raymond L. |
Orofino
Moscow
Orofino
Hindmarsh |
ID
ID
ID |
US
US
US
AU |
|
|
Family ID: |
70326188 |
Appl. No.: |
16/173369 |
Filed: |
October 29, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F42B 5/26 20130101; F42B
10/38 20130101; F42B 5/025 20130101 |
International
Class: |
F42B 5/26 20060101
F42B005/26; F42B 5/02 20060101 F42B005/02; F42B 10/38 20060101
F42B010/38 |
Claims
1. A centerfire rifle cartridge, comprising: a case having a head
end, an open mouth end for receiving a projectile, a central axis,
and an axial length measured along the central axis, the head end
having a base portion up to 0.804 inches in diameter; the case
having a case wall, the case wall having a taper of 0.85.degree. to
1.0.degree. relative to the central axis, a frusto-conical shoulder
portion extending from the case wall and having an angle of
35.degree. to 45.degree. relative to the central axis, and a neck
portion extending from the shoulder portion; and the neck portion
having a mouth sized to receive a .375 caliber projectile.
2. The cartridge of claim 1, wherein the case has a total axial
length in the range of about 3.24 inches to about 3.29 inches.
3. The cartridge of claim 1, wherein the wall has an axial length
from the head end of about 2.50 inches.
4. The cartridge of claim 1, wherein the case wall taper is about
0.9.degree. relative to the central axis.
5. The cartridge of claim 1, wherein the case capacity is greater
than 200 grains H.sub.2O.
6. The cartridge of claim 5, wherein the case has a capacity in the
range of about 210-230 grains H.sub.2O.
7. The cartridge of claim 1, further comprising a projectile having
a weight in the range of about 350-410 grains
8. The cartridge of claim 7, wherein the loaded overall length is
at least 4.65 inches.
9. The cartridge of claim 8, wherein the loaded overall length is
about 4.825 inches.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 62/580,476, filed Nov. 2, 2017, and incorporates
the same herein by reference.
TECHNICAL FIELD
[0002] This invention relates to a firearm cartridge and barrel
chamber for it. More particularly, it relates to a cartridge and
cartridge load combination for efficient, high-velocity,
long-range, precision shooting.
BACKGROUND
[0003] Ballistics, the science and study of projectiles and
firearms, may be divided into three categories. These are: interior
ballistics, exterior ballistics, and terminal ballistics. Interior
ballistics relates to the propulsion of a projectile, through the
bore of a barrel, to achieve a determined velocity as it leaves the
muzzle of the barrel. Exterior ballistics relates to the flight of
the projectile and how that flight is affected by its shape, its
velocity, and external forces, including wind and gravity. Terminal
ballistics relates to what effect the projectile has on the target
it strikes.
[0004] A projectile may be selected for the desired effect on its
intended target and the range it must travel from the firearm to
engage the target. One of the most critical factors on external
ballistic performance is the ballistic coefficient (BC) of the
projectile. The BC of a bullet is a measure of its ability to
overcome air resistance in flight. The drag coefficient of a
particular bullet shape and mass will vary depending on its
velocity. Propelling a bullet with a high BC at the highest
achievable velocity will provide the best exterior ballistics
performance, i.e., the "flattest" trajectory, for long range
shooting. Muzzle velocity is determined by interior ballistics
performance.
[0005] An ammunition cartridge "load" is a combination of the
selected cartridge case, powder propellant charge, primer, and
projectile (or bullet). The performance of a cartridge load is
determined by the combination of the shape and size of the
cartridge case, the powder propellant used (including burn rate and
pressure), and the size, shape, and mass of the projectile. Once a
projectile has been selected, several parameters influence the
interior ballistics of an ammunition load. The shape and dimensions
of the cartridge shell or case (relative to the interior bore
dimensions of the gun chamber), the amount and characteristics of
the propellant (powder) charge, the primer, and the primer vent
connection to the main cartridge chamber, and barrel length are
primary aspects of interior ballistics performance, for a
projectile of a given mass, that determine muzzle velocity.
Pressure and head space parameters are also important, and they
must be balanced against the other parameters.
[0006] The cartridge case is a hollow cylinder with a head end and
a projectile-receiving end. In "bottle-necked" cartridges, the
cylinder includes a generally cylindrical body portion extending
from the head end to a frusto-conical shoulder. The body portion
has a central opening in the head end for a primer and an annular
cartridge extraction groove formed adjacent the head end. The
frusto-conical shoulder is integrally formed with the body and
tapers from the body portion to a generally cylindrical integrally
formed neck portion. The neck portion extends longitudinally from
the shoulder portion and has a diameter smaller than the diameter
of the body portion with an open mouth for receiving and holding
the projectile.
[0007] While cartridge cases or shells theoretically may have any
combination of dimensions, there are several reasons why cartridges
are limited in their dimensions. The characteristics of gun powder
and structural limitations on rifle actions (which define the
chamber) make many extreme dimensional ratios impractical or
unsafe. Likewise, changes in the case geometry can change the rate
at which a powder burns and/or the chamber pressure produced in
unpredictable ways. Performance is not always a predictable
extrapolation from known data taken from existing cartridges and
can produce unexpected results in practice that differ from
theoretical or extrapolated calculations. Combinations that are
possible to construct may exhibit impractical and/or unexpected
characteristics. For example, they may cause extraordinary barrel
wear, may produce unexpected chamber pressures, or affect the metal
case in a way that shortens its useful life (number of times it can
be reloaded safely).
[0008] Another limitation is the rifle action (receiver and bolt)
into which the cartridge will be chambered and from which the
projectile will be propelled (through the barrel bore). A
bolt-rifle's action has an elongated opening aft of the chamber
through which a cartridge is received. The length of this opening
limits the cartridge overall length (OAL) that can be inserted.
This opening length essentially defines the length of the action.
The width of the action opening and bolt face diameter limits the
diameter of the accepted cartridge(s). Typically, a rifle bolt can
be made to fit an action length in a limited range of bolt face
diameters to accommodate the base diameter of a cartridge. Thus,
actions are produced in only a limited number of action groups or
"classes."
[0009] In these standard groups, a "short action" accepts a
cartridge with a maximum OAL of 2.84 inches and, in standard width,
a maximum diameter of 0.473 inch. This is sized to receive the 308
Winchester cartridge, for example. A "long action" closely accepts
a cartridge with a maximum OAL of 3.34 inches and, in standard
width, a maximum diameter of 0.473 inch. This is sized to receive
the .30-'06 Springfield cartridge, for example. A "magnum action"
accepts a cartridge with a maximum OAL of 3.681 inches and a
maximum diameter of 0.588 inch. This is sized to optimally receive
up to the .338 Lapua Magnum cartridge, for example. A "BMG action"
or "50 BMG action" accepts a cartridge with a maximum OAL of 5.54
inches and a maximum diameter of 0.804 inch. This is sized to
receive the .50 BMG and .416 Barrett, for example.
[0010] The .50 caliber BMG (Browning Machine Gun) was developed
from John Browning's design in 1917. The original loading was an
800 grain bullet fired at a velocity of 2,650 feet per second (fps)
out of a 46'' barrel. It was later loaded with a 900 grain bullet
fired at 2,500 fps. In recent decades, the .50 BMG has gained
popularity among civilian shooters as a 1,000+ yard target rifle.
Currently, the .50 BMG is commonly loaded with a 650 grain bullet
fired at 3,000 fps. It is designed to be effective past 2,000
meters or 2,500 yards.
[0011] There are several practical limitations to improving the
performance of cartridge loads for the .50 BMG. First, its case has
a very large powder capacity (more than 290 grains H.sub.2O or
almost 19 cm.sup.3). Less powder volume is needed with modern
propellants, meaning the case may only be partially filled and only
slow-burning powders can be effectively used. Empty space inside
the case allows the powder to be positioned differently from one
shot to the next, often resulting in velocity variations. Empty air
space in a partially filled case can affect how the powder burns, a
significant effect resulting from the empty space not being found
at the end of the case nearest the projectile. Instead, since a
rifle is likely to be fired at an angle near horizontal, the empty
space could unevenly extend the length of the case, unpredictably
affecting how the powder is ignited by the primer and how the burn
spreads through the case.
[0012] A cartridge known as the .416 Barrett (10.6.times.83 mm)
addressed some of these limitations. Using the .50 BMG as its
parent case, it was shortened and necked-down to accept a .416
caliber bullet. This reduced the case capacity to about 200 grains
H.sub.2O (13 cm.sup.3) and allowed a 398 grain (gr) bullet to be
propelled at an average of 3,150 fps from a 32-inch barrel.
[0013] There are various original design cartridges that have used
a .375 caliber projectile, including the .375 Belted Rimless
Nitro-Express (by Holland & Holland), the .375 Holland &
Holland Magnum, and the .378 Weatherby Magnum. Since then, various
cartridges loading a .375 caliber bullet have been developed from
parent cartridges in the "magnum" family, such as the .375 Ruger
and the .376 Steyr, and the .375 Lethal Magnum, using a belted
case. Previously, a .375 caliber cartridge has not successfully
been produced from a parent cartridge in the 50 BMG family.
SUMMARY OF THE INVENTION
[0014] The present inventors set out to develop a center-fire
cartridge load and bullet combination that would produce a
predictable shot out to at least 5,000 yards (4,572 meters). The
present invention can utilize a .416 Barrett case as its parent,
whose base is the same as that of a .50 BMG cartridge,
reconfiguring the geometry of the case with a higher angle shoulder
and a neck to seat a .375 caliber (9.5 mm) projectile having a mass
in the range of 360 grains to over 400 grains, for use in a 50 BMG
class action. The case configured according to one embodiment of
the present invention has a shoulder angle of approximately
40.degree. and provides an average case capacity of about 220
grains H.sub.20 (about 14.4 cm.sup.3) and cartridge overall length
(OAL) of 4.825 inches.
[0015] The sharper 40.degree. shoulder angle provides longer case
life than shallower angles due to reduced material flow during peak
pressures. With traditional 20.degree.-30.degree. shoulder angles,
internal pressures cause the brass case to "flow" forward,
resulting in thin necks and shoulder junctions. Thin spots
eventually result in cracked cases that are no longer usable for
reloading. The .416 Barrett cartridge, for example, has a
25.degree. shoulder angle, while the .50 BMG cartridge has a
shoulder angle of slightly under 16.degree. (15 degrees, 44
minutes). The present cartridge has been found to be reloadable at
least four times without annealing or trimming. The expectation is
that it can be reloaded at least eight times, with necessary
annealing and trimming procedures, without diminished
performance.
[0016] With large cases, over-pressuring often results in the
inability to extract fired brass from the chamber. Unlike an
"Ackley Improved" 40.degree. shoulder, which reduces body taper to
maximize case capacity, the body taper in the present design may be
maintained at approximately 0.9.degree..
[0017] The result is an advancement in the art that provides a
long-range, precision centerfire rifle cartridge capable of
propelling a projectile having optimum external ballistic
characteristics to a higher muzzle velocity, as well as other
unexpected and unpredictable benefits. The cartridge does not
perform according to internal/external ballistic calculation
predictions for the amount of propellant and weight/BC of the
projectile. Instead, its performance mimics that of a projectile
weighing 20% less. Measured muzzle velocities have averaged
3,150-3,200 fps with a 361 grain bullet from a 34 inch barrel,
which stays at supersonic speed beyond 3,000 yards. A 38 inch
barrel is calculated to allow the same projectile to achieve at
least 3,300 fps.
[0018] Other aspects, features, benefits, and advantages of the
present invention will become apparent to a person of skill in the
art from the detailed description of various embodiments with
reference to the accompanying drawing figures, all of which
comprise part of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Like reference numerals are used to indicate like parts
throughout the various drawing figures, wherein:
[0020] FIG. 1 is a side elevation view of a cartridge with seated
bullet according to an embodiment of the invention, partially cut
away to show cross-section of base and case wall;
[0021] FIG. 2 is a side view thereof showing dimensional
specifications thereof;
[0022] FIG. 3 is a chamber reamer specification drawing (not to
scale) for the cartridge embodiment; and
[0023] FIG. 4 is a side view of a projectile according to an
embodiment of the invention.
DETAILED DESCRIPTION
[0024] With reference to the drawing figures, this section
describes particular embodiments and their detailed construction
and operation. Throughout the specification, reference to "one
embodiment," "an embodiment," or "some embodiments" means that a
particular described feature, structure, or characteristic may be
included in at least one embodiment. Thus, appearances of the
phrases "in one embodiment," "in an embodiment," or "in some
embodiments" in various places throughout this specification are
not necessarily all referring to the same embodiment. Furthermore,
the described features, structures, and characteristics may be
combined in any suitable manner in one or more embodiments. In view
of the disclosure herein, those skilled in the art will recognize
that the various embodiments can be practiced without one or more
of the specific details or with other methods, components,
materials, or the like. In some instances, well-known structures,
materials, or operations are not shown or not described in detail
to avoid obscuring aspects of the embodiments.
[0025] Referring first to FIG. 1, therein is shown a firearm
cartridge 10 according to one embodiment of the present invention.
As found in all fixed ammunition, the cartridge 10 is generally
symmetrical around a central axis and comprises a case 12, which
provides generally cylindrical walls 14 axially extending from a
base portion 16. The base portion 16 includes an annular exterior
grove 18 that defines a rim 20 for extraction according to
well-known means from a firearm chamber. The base portion 16
includes a primer pocket 22 formed in the head 24 of the base
portion 16. The primer pocket 22 is connected through a flash hole
26 to a propellant-holding powder chamber 28 defined between the
walls 14 of the case 12. Axially spaced from the base portion 16,
the case walls 14 include a frusto-conical shoulder portion 30 at
which the diameter of the case 12 is significantly reduced and
transitions into a neck portion 32. The neck portion 32 holds or
seats a projectile (bullet) 34.
[0026] Referring now to FIG. 2, dimensional aspects of this
embodiment of the cartridge 10 are shown. The cartridge case 12 and
seated projectile 34 are substantially symmetric about their
longitudinal axis a. The projectile 34 for this embodiment is a
.375 caliber solid bullet, which will be described in greater
detail below. The case 12 includes a base portion 16 with
dimensions consistent with those of a .50 BMG cartridge (and those
of a .416 Barrett cartridge). The .416 Barrett case may be used as
the "parent" for the case 12 of the present invention. Likewise,
the .416 Barrett is derived from the case of a .50 BMG cartridge.
Thus, all dimensions associated with the base portion 16 of the
case 12 may be substantially the same as these other rounds. The
case 12 is significantly shorter than that of the .50 BMG and
differs significantly from those of the .416 Barrett. Specifically,
the angle of the shoulder portion 30 is significantly steeper at
about 40.degree.. The transition zones between the case wall 14,
shoulder portion 30, and neck portion 32 may be formed with a
somewhat rounded radius according to the "Ackley improved"
specifications. However, unlike a "full Ackley improved"
modification, which generally removes any taper from the case wall
14 to maximize powder capacity, the cartridge 10 of the present
invention retains a cartridge wall taper of up to 1.degree., with
the preferred taper being at about 0.9.degree.. The neck can be
shortened, but the full length allows better adjustment of seating
depths for projectiles. As will be discussed in greater detail
below, the primer pocket 22 is sized to receive a .50 BMG-size
primer. As previously described, the 40.degree. shoulder angle
reduces material flow of the case 12, when fired, and, as will be
discussed in greater detail below, affects the propellant burn
rate, chamber pressure, and projectile velocity.
[0027] Referring now also to FIG. 3, therein is shown a
specification drawing for a chamber reamer to receiver the
cartridge 10 of this embodiment in a barrel having a nominal .375
caliber bore. Note that the drawing of FIG. 3 is a schematic
representation of dimensions and is not illustrated to scale. When
a cartridge 10 according to this embodiment of the invention is
fired in a chamber formed according to the reamer specifications
shown in FIG. 3, the case 12 will be expanded ("fire formed") by
the internal pressure of the burning propellant and may force the
above-described rounded transitions at the shoulder portion 30 into
the more sharply defined dimensions of the barrel chamber.
According to well-known methods, a previously fired case 12 may be
resized to original specifications and reloaded.
[0028] Projectiles are commercially available in .375 caliber
having a weight as low as 350 grains or as high as 452 grains. Of
course, heavier projectiles have a higher ballistic coefficient,
but require greater energy to achieve muzzle velocities necessary
to maintain supersonic speed and stability for greater distances. A
variety of .375 caliber projectiles 34, typically machined from
solid copper and having a mass in the range of 350 to 400 grains,
or above, may be utilized with successful results. Three example
projectiles are described in greater detail below.
Example 1
[0029] A Flat Line.TM. .375 caliber bullet made by Warner Tool
Company of North Swanzey, N.H., provides a 361 grain, solid copper
bullet having a 2.20 inch overall length (OAL). This projectile
includes a 16.degree. boat tail and may be made in accordance with
the invention described in U.S. Patent Application Publication No.
2016/0327380, published Nov. 10, 2016, the contents of which are
hereby incorporated herein by reference. This projectile has
ballistic coefficients (BC) acoustically measured in the range of
3,000 to 15,000 fps of G1BC=0.980 and G7BC=0.494. Ballistic
coefficients measured by Doppler radar chronograph of G1BC=0.961
and G7BC=0.480. The minimum twist recommended for this projectile
is 1:10 inches. The inventors have found a preferred twist rate of
1:8.65 inches to 1:8.75 inches. This example is illustrated in FIG.
4.
Example 2
[0030] A non-standard 400 grain, .375 caliber, solid copper bullet
made by Berger Bullets LLC of Fullerton, Calif. Sample projectiles
have a calculated BC greater than 1.0 (about 1.1). Warner Tool
Company, referenced above, also makes a 400 grain, .375 caliber
projectile that is suitable.
Example 3
[0031] A MTAC.TM. (match/tactical) 3.745/.3655 caliber, 402 grain,
solid copper projectile made by Cutting Edge Machining Solutions
Inc., d/b/a Cutting Edge Bullets, of Drifting, Pa., having a
G1BC=0.990 and OAL of 2.209 inches. This projectile requires a
twist of 1:7.5 inches or faster.
[0032] A primer (well-known, not shown) sized to seat in a primer
pocket 22 configured for .50 BMG-size primers may be used. The
geometry of the case 12 of the present invention provides maximum
performance using a medium-slow burning powder, generally in the
category of those designed for the .338 Lapua Magnum or .50 BMG
cartridges. H50BMG or similar powders may be used. A powder
designed for the .338 Lapua Magnum cartridge having a burn rate
only slightly faster than powder intended for .50 BMG cartridge may
provide better performance. For example, 168 grains of Reloder.RTM.
33 propellant powder by Alliant Powder of Anoka, Minn., has been
used in the cartridge 10 of the present invention to propel a 361
grain projectile through a 34 inch barrel to an average muzzle
velocity in the range of 3,150 to 3,200 fps. As previously
described, the burn rate of propellant powders has been found to be
different than predicted by the powder manufactures. Likewise,
performance of the cartridge has been found to be different than
predicted due to the novel case geometries and projectile caliber
combinations.
[0033] The cartridge 10 is accommodated by a 50 BMG-class action
and bolt, the case 12 having substantially the same base and head
dimensions of a .50 BMG cartridge and a shorter OAL. Chamber
pressures produced are within ranges safely accommodated by a 50
BMG-class action, bolt, and barrel.
[0034] As described above, unexpected performance has been produced
using a 34 inch barrel in .375 caliber. The performance has been
found to mimic that of the calculated performance of a projectile
weighing 20% less. Using this adjusted performance calculation, it
is expected that a 361 grain projectile could exceed 3,300 fps from
a 38 inch barrel. Using a twist rate of 1:8.65 inches, the
projectile stays supersonic past 3,000 yards, with the expectation
of targetable flight to at least 5,000 yards.
[0035] While one or more embodiments of the present invention have
been described in detail, it should be apparent that modifications
and variations thereto are possible, all of which fall within the
true spirit and scope of the invention. Therefore, the foregoing is
intended only to be illustrative of the principles of the
invention. Further, since numerous modifications and changes will
readily occur to those skilled in the art, it is not intended to
limit the invention to the exact construction and operation shown
and described. Accordingly, all suitable modifications and
equivalents may be included and considered to fall within the scope
of the invention, defined by the following claim or claims.
* * * * *